Abstract
Plant immunity depends on massive expression of pathogenesis-related genes (PRs) whose transcription is de-repressed by pathogen-induced signals. Salicylic acid (SA) acts as a major signaling molecule in plant immunity and systemic acquired resistance triggered by bacterial or viral pathogens. SA signal results in the activation of the master immune regulator, Nonexpressor of pathogenesis-related genes 1 (NPR1), which is thought to be recruited by transcription factors such as TGAs to numerous downstream PRs. Despite its key role in SA-triggered immunity, the biochemical nature of the transcriptional coactivator function of NPR1 and the massive transcriptional reprogramming induced by it remain obscure. Here we demonstrate that the CBP/p300-family histone acetyltransferases, HACs and NPR1 are both essential to develop SA-triggered immunity and PR induction. Indeed HACs and NPR1 form a coactivator complex and are recruited to PR chromatin through TGAs upon SA signal, and finally the HAC−NPR1−TGA complex activates PR transcription by histone acetylation-mediated epigenetic reprogramming. Thus, our study reveals a molecular mechanism of NPR1-mediated transcriptional reprogramming and a key epigenetic aspect of the central immune system in plants.
Highlights
Plants lack specialized immune cells, they have developed sophisticated defense systems against pathogenic attacks
We and others have found that histone H3 acetylation (H3Ac) at the Arabidopsis PR1 locus is increased by pathogen attack or Salicylic acid (SA) treatment, and this increase is tightly associated with PR1 transcription [35,49,50,51]
As H3Ac acts as an active epigenetic mark, first we searched for Arabidopsis histone acetyltransferases (HATs) mutants with impaired PR1 and PR2 induction upon 2,6dichloroisonicotinic acid (INA; synthetic SA analog) treatment
Summary
Plants lack specialized immune cells, they have developed sophisticated defense systems against pathogenic attacks. Salicylic acid (SA), a key signaling molecule in plant immunity [1,2], induces a transcription reprogramming through the master immune-regulator Nonexpressor of pathogenesis-related genes 1 (NPR1) [3,4,5,6]. CBP/p300-family histone acetyltransferases (HATs) are well-known transcriptional coactivators that control a variety of differentiation and developmental processes. They facilitate transcription by diverse functions: relaxing chromatin structure through histone acetylation [21,22,23], modulating the activity of transcriptional regulators through acetylation [24,25,26], acting as adaptor for numerous transcription factors [27,28] and bridging transcription factors to transcription machineries [29,30]. Multiple morphological and developmental defects were observed in Arabidopsis mutants lacking multiple HACs, so far only a few studies have reported in-depth physiological analyses on these mutants and revealed the molecular functions of HACs in flowering and ethylene signaling [31,33]
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